diff --git a/src/lib/guesser/reducing.ts b/src/lib/guesser/reducing.ts
index 0fdce95..bb88f78 100644
--- a/src/lib/guesser/reducing.ts
+++ b/src/lib/guesser/reducing.ts
@@ -157,7 +157,24 @@ Deno.test("test_smallest_cuts", () => {
 	assertEquals(best, "ba");
 });
 
-function matches_constraints(cand: string, constraints: [string, Info][]) {
-	// TODO
-	return false;
+function matches_constraints(candidate: string, constraints: [string, Info][]) {
+	const letters = [...candidate];
+
+	for (const [index, [letter, info]] of enumerate(constraints)) {
+		if (info.kind !== "there") continue;
+		if (letters[index] !== letter) return false;
+		letters[index] = ".";
+	}
+
+	for (const [index, [letter, info]] of enumerate(constraints)) {
+		if (info.kind === "there") continue;
+		if (info.kind === "abscent") if (letters.includes(letter)) return false;
+		// is somewhere
+		if (letters[index] === letter) return false;
+		if (!letters.includes(letter)) return false;
+		const index_ = letters.findIndex((i) => i === letter);
+		letters[index_] = ".";
+	}
+
+	return true;
 }